Diwali: The Cause of Peak Pollution?

Since the time part 1 of this article was published, the Supreme Court of India has reversed an earlier judgement made on the 12th of September and gone ahead and banned sale of firecrackers till the 1st of November 2017. In its judgement, the honorable Court has stated that it wants to ‘test’ the effect of the ban on firecrackers on Diwali days to see if there is a reduction in pollution. It also suggested that the basis for an order targeting Diwali days for the experiment to be the ‘virtual consensus’ in the country.

The underlying assumption in the order of the Court is that the maximum amount of pollution is caused on actual Diwali days, and hence the focus on banning firecrackers sale to reduce the “spike” of pollutants on Diwali days. In the previous article, it has been shown that the peak particulate matter levels in the 2013 were not on Diwali day but a few weeks after Diwali. Similarly, the article had also highlighted that the noise pollution levels on Diwali days is not significantly different from other days.

The Supreme Court order indicated high levels of particulate matter on Diwali days. It also quoted a Central Pollution Control Board (CPCB) submission that the levels of Sulphur Dioxide reach an unacceptably high level on Diwali days.

Since the earlier article focused on 2013 data, we decided to gather more recent data and test whether the hypothesis made by the honorable Supreme Court was true.

From the website of the CPCB, we gathered data for 3 main pollutants – ParticulateMatter10 (PM10), ParticularMatter2.5 (PM2.5) and Sulphur Dioxide (SO2) for the entire year 2016. Further, the data for these pollutants were obtained for as many sites for which data was available online. Thus, for PM10, data from 4 sites were downloaded. For PM2.5 and SO2, data from 6 sites were downloaded.

Using the data, 2 kinds of charts were drawn up. The first set of charts plotted the pollutant values against the day of the year. So the X axis shows the number of days since the beginning of the year and the Y axis shows the 24 hours average value of the pollutant on that day.

Diwali day happens to be day 304 in the year 2016. This is marked with a pink bar in all the charts. There are 3 horizontal lines drawn in each chart. The green horizontal line shows the safe limit for the particular pollutant. The black horizontal line shows the 2X limit for the pollutant and the red horizontal line shows the 2SD (standard deviations) for the same pollutant.

Particulate Matter 10 charts

In order to better observe the data around Diwali, we have prepared a second set of charts for the same data-set in which we zoom in on the data for the 2 months around Diwali. The three purple lines in this chart represent the 3 days of Diwali (29, 30 and 31 of October 2016)

Here are the charts for PM10

Some key observations from the above chart:

The peak PM10 value for the entire year is on Diwali day at two of the four locations (RK Puram and Anand Vihar) while at the other two locations it is not on Diwali day. This comes out clearly from the zoom-in charts.

At all locations, the PM10 levels are above 2X levels on most days in the year, indicating a severe problem which is not primarily created due to firecrackers.

There is a clear pattern of the PM10 values going extremely high in the last quarter of the year, between October to December. Again, this has no correlation with bursting of crackers on Diwali days.

Particulate Matter 2.5 chartsLet us now look at the zoom-in charts for PM2.5 for the same locations.The key observations from the above charts for PM2.5 are as follows

At all sites, the peak value of PM2.5 is never on the day of Diwali. Again, this fact comes out clearly from the zoom-in charts.

Just like in PM10, there is a huge clustering effect observed in the last quarter of the year. There is also a significant cluster seen during January-February, which clearly rules out Diwali firecrackers as being the main reason for the worsening of the particulate matter levels.

Sulphur Dioxide charts

Just like in the case of PM10 and PM2.5, let us look at the zoom-in charts for SO2 now.The observations from the charts related to SO2 are as follows:

Even on Diwali days, the SO2 levels are well within the safe limits.

The maximum value of SO2 in none of the locations happens to be on Diwali day.

There is a clear cluster that is formed during the months of April-May in all locations, indicating that the reason for high SO2 levels is not fireworks but perhaps increased burning of vehicle fuel (or some other reason)

Conclusion

From the above data, and analysis, it is quite clear that while there is an increase of particulate matter on the days of Diwali, it clearly is not the only reason for the high values. Further, in an overwhelming majority of the readings, the values of the pollutants on Diwali days are not even the highest in the year. The period between October and December is a period of high particulate matter accumulation in Delhi. Clearly, this indicates that the real reason for high particulate matter is something additional, and not just, or only, firecrackers due to Diwali.